Abstract
BackgroundLignin peroxidase (LiP) is the primary enzyme responsible for lignin degradation. In our previous work, in order to shorten the pretreatment time and increase the lignin degradation, we have pretreated the corn stalk (CS) using a combination of Aspergillus oryzae CGMCC 5992 solid-state fermentation and H2O2 treatment.ResultsIn the present study, one-factor-at-a-time design and response surface design were applied to optimize the nutritional constituents for LiP production in liquid-state fermentation by A. oryzae CGMCC 5992 and the conditions for CS degradation by A. oryzae CGMCC 5992. The optimal medium included CS of 30 g/L, glucose of 4.6 g/L, sodium nitrate of 1.2 g/L, corn steep liquor of 1 g/L, yeast extract of 1.2 g/L, and vitamin B1 of 0.15 g/L. Under these optimal conditions, the LiP production reached its maximum of 652.34 U/L. The optimal condition for CS degradation included CS of 20 g, A. oryzae CGMCC 5992 broth of 50 mL, 1.5 % H2O2 solution of 80 mL, H2O2 flow rate of 0.4 mL/min, water volume of 240 mL (water/material ratio of 12:1), hydrolysis temperature of 39 °C, and hydrolysis time of 8 h. Before hydrolysis, CS and water were pretreated at 113 °C for 11 min. Under these optimal conditions, the sugar yield reached its maximum of 46.28 %.ConclusionsOur newly developed method had great advantages in pretreatment of CS due to its quickness, convenience, safety, no special equipment and high sugar yield.Graphical abstractThe schematic diagram of corn straw hydrolysisElectronic supplementary materialThe online version of this article (doi:10.1186/s13068-015-0362-4) contains supplementary material, which is available to authorized users.
Highlights
Lignin peroxidase (LiP) is the primary enzyme responsible for lignin degradation
We have studied the possibility of using A. oryzae CGMCC 5992 to degrade lignin of corn stalk (CS) pretreated with different concentrations of H2O2 in the solid-state fermentation, and we have found that A. oryzae can grow well on CS pretreated with 3 % H2O2
LiP activity was used as an index to optimize the fermentation condition of A. oryzae
Summary
In order to shorten the pretreatment time and increase the lignin degradation, we have pretreated the corn stalk (CS) using a combination of Aspergillus oryzae CGMCC 5992 solid-state fermentation and H2O2 treatment. Straws from cereal crops are the major by-product from agricultural fields in China. Lignin, hemicellulose, and cellulose are the three major chemical components of corn stalk (CS). As a macromolecule and highly branched polymer, lignin forms the lignin sheath and surrounds hemicellulose and cellulose, which protects the cellulose and hemicellulose from degradation by cellulase and hemicellulase [2,3,4]. The crystal structures of cellulose and hemicelluloses cause difficulties to fully swell like starch in the process of high-temperature pretreatment, leading to the reduced access surface areas and the limited degradations of cellulase and hemicellulase.
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